1. Field of the Invention
The present invention relates to a printing device and method including a liquid developing device, a liquid developing method and a related printer including the device, and more particularly, to a liquid developing device which can retain an ink concentration and ink amount for use during printing.
2. Description of the Related Art
A liquid developing device forms a developing unit included in a wet-type electrophotographic printer, such as a printer, copier, facsimile device, for example. The liquid developing device includes a storage tank which stores ink, which is a mixture of toner and carrier, and supplies a developing unit with the stored ink. The developing unit develops an electrostatic latent image formed on a photoconductor belt with the ink. The toner included in the ink is attracted onto the photoconductor belt by electric charge. The toner travels inside the carrier, is adhered onto the photoconductor belt, and forms a toner image corresponding to the electrostatic latent image. The toner image is transferred onto a paper so as to form a desired image thereon.
The ink which includes the toner remaining after being used for developing the image is collected into the storage tank. The collected ink mainly includes carrier, thus the concentration of the ink in the storage tank becomes low. The liquid developing device uses ink, whose concentration is 3% and volume is 400 ml, for example. In this case, if the liquid developing device successively prints a predetermined image onto 400 to 500 papers with printing density of 5%, the concentration of the ink becomes lower than 2%. Thus, the printing can not be properly accomplished. The concentration of ink indicates the weight percentage of toner included in the ink. The printing density indicates the percentage of an area occupied by an output image in the entire printing area on the paper.
Some carrier is adhered onto the photoconductor belt without being collected into the storage tank. This results in a decrease in the amount of ink inside the storage tank, hence failing in printing performance.
In this structure, hence, the liquid developing device needs to adjust the concentration and amount of the ink stored in the storage tank. Such a liquid developing device is disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H11-184258. When the concentration of the ink stored in the storage tank is equal to or lower than a predetermined level, the liquid developing device discharges the stored ink, and adds concentrated ink and carrier, thereby to keep a predetermined amount of the ink stored in the storage tank.
While adjusting the concentration of the ink, the liquid developing device needs to suspend the printing operation. That is, the adjusting and the printing can not be performed at the same time. Hence, if the concentration of the ink gets lower while successively developing images onto a large number of papers, the liquid developing device adjusts the concentration during the suspension of the developing. Hence, the printing is achieved only with low efficiency.
Generally speaking, some colors of inks are more likely to be used. Thus, if the adjustment of the concentration is not successfully performed before the developing, an image is output with the frequently-used inks having insufficient concentration of toner. In consideration of this, if an arithmetic logic unit which can perform data processing speedily is employed in the liquid developing device, the problem is that the liquid developing device is manufactured at a high cost.
The present invention has been made in consideration of the above. It is accordingly an object of the present invention to provide a liquid developing device, adjusting a concentration and amount of ink while developing is still performed, a liquid developing device, and a printer including the device.
Another object thereof is to provide a liquid developing device, for reducing unevenness of toner colors at a low cost, a liquid developing device, and a printer including the device.
In order to achieve the above objects, according to the first aspect of the present invention, there is provided a liquid developing device comprising:
a storage tank which stores an ink, including a toner and a carrier, for developing an electrostatic latent image on a photoconductor;
an ink supply pump which sends an ink from the storage tank to the photoconductor;
a concentration sensor which measures a toner concentration of the ink to be sent to the photoconductor;
a storage-amount sensor which measures an amount of ink stored in the storage tank;
a concentrated-ink supply pump which sends a concentrated ink from an ink cartridge for storing an concentrated ink to the storage tank;
a carrier supply pump which sends a carrier from a carrier cartridge for storing a carrier to the storage tank;
an ink discharge pump which discharges an excessive ink from the storage tank to a discharge cartridge; and
a controller which controlls the concentrated-ink supply pump, the carrier supply pump, and the ink discharge pump, so as to retain a predetermined level of the toner concentration of the ink stored in the storage tank and a predetermined amount of the ink, based on a measurement value from the concentration sensor and a measurement amount from the storage-amount sensor.
According to the above structure, the ink supply pump sends the ink from the storage tank to the photoconductor. The concentrated-ink supply pump sends the concentrated ink to the storage tank. The carrier supply pump sends the carrier to the storage tank. The ink discharge pump discharges the excessive ink from the storage tank. In this structure, the liquid developing device can develop the photoconductor with the stored ink, and can retain the predetermined levels of the toner concentration and the amount of the stored ink. Therefore, the liquid developing device can successively print with ink whose toner concentration is stably controlled.
The controller may supplement the storage tank with a concentrated ink using the concentrated-ink supply pump, supplement the storage tank with a carrier using the carrier supply pump, and discharge an excessive ink from the storage tank using the ink discharge pump, based on an error between a measurement value from the concentration sensor and a predetermined value of the concentration and an error between a measurement amount from the storage-amount sensor and a predetermined amount, so that the toner concentration of the ink stored in the storage tank and the amount of the ink approach the predetermined value of the concentration and the predetermined amount, respectively.
In the above structure, the controller stores a controlling program, so as to perform PID (Proportional Integration and Derivation) controlling, proportional controlling, proportional integration controlling, etc. based on the error between the measurement value sent form the concentration sensor and the predetermined value (target value). The controller can control each of the concentrated-ink supply pump, the carrier supply pump, and the ink discharge pump, so as to approach the error between the measurement value and the predetermined value and the error between the measurement amount and the predetermined amount to 0, in accordance with the controlling program.
The controller may drive each of the concentrated-ink supply pump, the carrier supply pump, the ink discharge pump, so as to supply a concentrated ink or a carrier to the storage tank, in accordance with at least one of the error between the measurement value from the concentration sensor and the predetermined value of the toner concentration, an integrated result of the error, and a differentiated result of the error, and to supply a concentrated ink and a carrier to the storage tank or to discharge an excessive ink from the storage tank, in accordance with at least one of the error between the measurement amount from the level sensor and the predetermined amount, an integrated result of the error, and a differentiated result of the error.
The controller may:
determine whether the measurement value from the concentration sensor is lower than the predetermined value;
supplement the storage tank with a concentrated ink using the concentrated-ink supply pump, when determined that the measurement value from the concentration sensor is lower than the predetermined value, and supplement the storage tank with a carrier using the carrier supply pump, when determined that the measurement value from the concentration sensor is higher than the predetermined value;
determine whether the measurement amount from the storage-amount sensor is lower than the predetermined amount;
supplement the storage tank with a concentrated ink and a carrier using the concentrated-ink supply pump and the carrier supply pump, when determined that the measurement amount from the storage-amount sensor is lower than the predetermined amount, and discharge an excessive ink from the storage tank using the ink discharge pump, when determined that the measurement amount from the storage-amount sensor is higher than the predetermined amount.
In order to achieve the above objects, according to the second aspect of the present invention, there is provided a liquid developing device comprising:
four storage tanks which respectively store fours colors, yellow, cyan, magenta, and black, of inks, each including a toner and a carrier, for use in developing an electrostatic latent image formed on a photoconductor;
four ink supply pumps which respectively send the four colors of inks from the respective storage tanks;
four concentration sensors which respectively measure toner concentrations of the respective four colors of inks to be sent to the photoconductor;
four storage-amount sensors which respectively measure amounts of four colors of inks stored in the respective storage tanks;
four concentrated-ink supply pumps which respectively send four colors of inks from ink cartridges to the respective storage tanks each of which stores a same color of ink as a color of a concentrated ink stored in one of four ink cartridges;
a carrier supply pump which sends a carrier to the storage tanks from a carrier cartridge storing a carrier;
four ink discharge pumps which respectively discharge excessive inks from the respective storage tanks to a discharge cartridge; and
a controller which controlls each of the concentrated-ink supply pumps, the carrier supply pump and the ink discharge pumps, so as to retain a predetermined level of the toner concentrations of the inks stored in the respective storage tanks and a predetermined amount of the inks stored therein, based on a measurement value form each of the concentration sensors and a measurement amount of each of the storage-amount sensors.
The controller may:
sequentially store measurement values measured by the respective concentration sensors and measurement amounts measured by the respective storage-amount sensors, and obtain a change rate of each of the respective measurement values and change rates of the respective measurement amounts, with respect to a predetermined time period;
discriminate an ink having a highest change rate among the change rates of other inks, based on combinations of the respective change rates of the toner concentrations and the respective change rates of the amounts of the inks which are stored in the respective storage tanks; and
control the toner concentration of the discriminated ink and the amount of the discriminated ink.
According to the above structure, the controller discriminates an ink whose toner concentration and amount show a sudden change. The controller then can control the toner concentration and amount of the discriminated ink. Therefore, in the case of successively printing images with an ink, when the printing density of the ink is high, the unevenness of the color inks can be reduced.
In order to achieve the above objects, according to the third aspect of the present invention, there is provided a printer comprising:
the liquid developing device of claim 1;
a photoconductor which is rotated by being driven by a driving roller;
a charger which charges the photoconductor with electricity;
an exposure device exposes the charged photoconductor to form an electrostatic latent image on the photoconductor;
a developing unit to which an ink is supplied from the liquid developing device, and which adheres the supplied ink onto a section of the photoconductor which is charged with electricity and on which the electrostatic latent image is formed;
a transfer roller which is rotated in synchronization with the photoconductor, and onto whose surface a toner on the photoconductor is transferred so as to transfer the toner onto a recording medium;
a fixation roller which is rotated in contact with the transfer roller between which the recording medium is sandwiched, melts the toner transferred onto the transfer roller, and fixes the melted toner onto the recording medium; and
a discharge roller which discharges the recording medium onto which the toner is fixed by the fixation roller.
In order to achieve the above objects, according to the fourth aspect of the present invention, there is provided a liquid developing method comprising:
supplying an ink from a storage tank, storing an ink including a toner and a carrier and for use in developing an electrostatic latent image formed on a photoconductor, to the photoconductor;
developing the photoconductor with the ink supplied by the supplying;
measuring a toner concentration of the ink which is to be sent to the photoconductor by the supplying;
measuring an amount of ink stored in the storage tank; and
controlling the toner concentration of the ink stored in the storage tank and the amount of the ink, by supplying the storage tank with a concentrated ink and a carrier, and by discharging an excessive ink from the storage tank, while developing the photoconductor by the developing, based on a measurement value measured by the measuring the toner concentration and a measurement amount measured by the measuring the amount.
The controlling may include
supplying a concentrated ink to the storage tank, supplying a carrier to the storage tank, and discharging an excessive ink from the storage tank, based on an error between the measurement value and a predetermined value of a toner concentration and an error between the measurement amount and a predetermined amount of ink, so as to approach the toner concentration of the ink stored in the storage tank and the amount of the stored ink to the predetermined value and the predetermined amount, respectively.
The controlling may include
supplying a concentrated ink to the storage tank, supplying a carrier to the storage tank, and discharging an excessive ink from the storage tank, so as to supply the storage tank with an amount of an ink or carrier, in accordance with at least one of the error between the measurement value and the predetermined value of the toner concentration, an integrated result of the error, and a differentiated result of the error, and to supply to or discharge from the storage tank an amount of a liquid, in accordance with at least one of an error between the measurement amount and the predetermined amount of the ink, an integrated result of the error, and a differentiated result of the error.
The controlling may include:
determining whether the measurement value which is measured by the measuring the concentration is lower than a predetermined value;
supplying the storage tank with a concentrated ink, when determined that the measurement value is lower than the predetermined value;
supplying the storage tank with a carrier, when determined that the measurement value is higher than the predetermined value;
determining whether the measurement amount which is measured by the measuring the amount is higher than a predetermined amount;
discharging an excessive ink from the storage tank, when determined that the measurement amount is higher than the predetermined amount; and
supplying the storage tank with a concentrated ink and a carrier, when determined that the measurement amount is lower than the predetermined amount.
In order to achieve the above objects, according to the fifth aspect of the present invention, there is provided a liquid developing method comprising:
supplying four kinds of inks, each of which includes a toner and a carrier, for use in developing an electrostatic latent image formed on a photoconductor, respectively from four storage tanks to the photoconductor;
developing the photoconductor with each of the four inks which are supplied by the supplying;
measuring a toner concentration of each of the inks to be supplied to the photoconductor by the supplying;
measuring an amount of each of the four inks included respectively in the storage tanks;
controlling the toner concentration of each of the four inks stored respectively in the storage tanks and the amount of each of the four inks, by supplementing each of the storage tanks with a concentrated ink an a carrier, and by discharging an excessive ink from each of the storage tanks, while developing the photoconductor by the developing, based on the measurement value measured by the measuring the toner concentration and the measurement amount measured by the measuring the amount.
The controlling may include:
sequentially storing the measurement values which are measured by the measuring the toner concentration and the measurement values which are measured by the measuring the amount;
obtaining a change rate, with respect to a predetermined time period, of each of the measurement values sequentially stored by the storing;
discriminating an ink having a highest change rate among the change rates of other inks, based on combinations of the respective change rates of the toner concentrations and the respective change rates of the amounts of the inks which are stored in the respective storage tanks; and
controlling the toner concentration of the discriminated ink and the amount of the discriminated ink.